CA1038481A - Transmission of radio navigation phase correction - Google Patents
Transmission of radio navigation phase correctionInfo
- Publication number
- CA1038481A CA1038481A CA203,817A CA203817A CA1038481A CA 1038481 A CA1038481 A CA 1038481A CA 203817 A CA203817 A CA 203817A CA 1038481 A CA1038481 A CA 1038481A
- Authority
- CA
- Canada
- Prior art keywords
- phase
- correction
- corrections
- receiver
- received
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S1/00—Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith
- G01S1/02—Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith using radio waves
- G01S1/08—Systems for determining direction or position line
- G01S1/20—Systems for determining direction or position line using a comparison of transit time of synchronised signals transmitted from non-directional antennas or antenna systems spaced apart, i.e. path-difference systems
- G01S1/30—Systems for determining direction or position line using a comparison of transit time of synchronised signals transmitted from non-directional antennas or antenna systems spaced apart, i.e. path-difference systems the synchronised signals being continuous waves or intermittent trains of continuous waves, the intermittency not being for the purpose of determining direction or position line and the transit times being compared by measuring the phase difference
- G01S1/308—Systems for determining direction or position line using a comparison of transit time of synchronised signals transmitted from non-directional antennas or antenna systems spaced apart, i.e. path-difference systems the synchronised signals being continuous waves or intermittent trains of continuous waves, the intermittency not being for the purpose of determining direction or position line and the transit times being compared by measuring the phase difference particularly adapted to Omega systems
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
- G01S5/02—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using radio waves
- G01S5/12—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using radio waves by co-ordinating position lines of different shape, e.g. hyperbolic, circular, elliptical or radial
Landscapes
- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Radar, Positioning & Navigation (AREA)
- Remote Sensing (AREA)
- Computer Networks & Wireless Communication (AREA)
- Position Fixing By Use Of Radio Waves (AREA)
- Mobile Radio Communication Systems (AREA)
Abstract
ABSTRACT
A method of and apparatus for navigation in diffeRential-mode in a sequential system for radio-navigation by phase reception. In transmission an amplitude-modulated radiogoniometric carrier wave is modulated in phase or frequency, this modulation being effected by a low-frequency subcarrier signal which is itself so modulated in phase sequentially in accordance with the phase corrections that each phase correction appears approximately simultaneously with the phase concerned. At a standard radionavigation receiver, the subcarrier signal modulated by the corrections is re-covered, and the phase corrections are so applied to the received phases that each phase undergoes the phase correction received at the same instant.
A method of and apparatus for navigation in diffeRential-mode in a sequential system for radio-navigation by phase reception. In transmission an amplitude-modulated radiogoniometric carrier wave is modulated in phase or frequency, this modulation being effected by a low-frequency subcarrier signal which is itself so modulated in phase sequentially in accordance with the phase corrections that each phase correction appears approximately simultaneously with the phase concerned. At a standard radionavigation receiver, the subcarrier signal modulated by the corrections is re-covered, and the phase corrections are so applied to the received phases that each phase undergoes the phase correction received at the same instant.
Description
: ~0384fll The invention concerns an aid to navigation in a sequential system of radionavigation by phase reception which : is used in differential mode of operation, such as the system ; 5 known under the name O~GA, and which is envisaged for ; general application on a terrestrial scale.
It is known that the differential-mode use of a radio-navigation system presumes supplementary transmission of phase corrections defined by the difference between each phase .,.: .
10 received at a selected site and the corresponding theoretical phase. The theoretical phase at a point is that which, in the - theoretical network of position lines, satisfies a reciprocal and stationary correspondence with the geographical position of this point. ~he received phase varies complexly with time 15 in relation to the theoretica1 phase, and this produces untimely errors in this reciprocal correspondence. It is therefore apparent that the knowledge of the corrections thus transmitted permits substantial reduction of these untimely errors.
This differential usage applies only in a certain zone -~
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close to the selected site. It is therefore desirable that the supplementary transmission should be extended to this zone, whatever type of receivers of the sequential radio-navigation system are to be found there.
For the same reason, a large number of supplementary transmissions of this kind also need to be provided if the differential-mode radionavigation system is desired for use _ _ . , :, 10384fll over long distances. In particular, in coastal areas the supplementary phase-correction transmissions should be made in sufficient number to enable the differential-mode radio-navi~ation system to be used along all coast and thereby obtain the advantage of greater precision.
The radionavigation system receivers intended for additionally receiving this correction transmission can, for their part, range from the ordinary type to the highest degree of precision according to the application. Also it is ... . .
clearly necessary for the same correction receiver to be usable over great distances for a full set of these supple-mentary transmissions and without involving the user in -complicated operations. In other words, an intervening normalization is required over the set of supplementary phase correction transmissions. -Each correction transmitting station has therefore to allow general diffusion over a certain zone for receivers which range from the ordinary t~pe to the greatest precision, more generally, a large number of such transmitting stations have to satisfy this criterion, while at the same time permitting a normalization of utilization and great precision.
In the case of the Omega system, for example, eight base transmitting stations are provided to cover all the globe, the distance between transmitting stations here being of the order of 8000 km (5000 miles).
According to present estimates, the utilization range ; of one correction transmittinD station will at most be several -- , : ~, .............................................. .
. ~
~ , .. . ... . .. ~ .
1 hundred kilometers. It is therefore clear that a considerable number of correction transmitting stations is required.
Having regard to the present congestion of the ether, frequency allocations are becoming increasingly more difficult . .
to obtain for differential radionavigation, even with ~ technical requirements as fundamental as those which have ;~ just been presented.
In the future it seems unlikely that the allocation of new radio channels will be sufficient to solve this problem, for it will probably be necessary to install progressively more and more correction transmitting stations, and this will quickly saturate these new channels.
Moreover it is clear that most of the channels already occupied are not compatible with all the requirements set out above for the supplementary transmission of corrections, namely, diffusion over predetermined zones, great simplicity or utilization, normalization over a large number of different transmissions and high precision.
However the present invention contributes a parti-cularly satisfying solution to the problem thus posed.
According to the invention, a method of aid to navi-gation is provided for use in differential mode in a sequential system of radionavigation by phase reception.
In transmission, a radiogoniometric carrier wave - amplitude modulated as an identification code, is modulated in phase or frequency by a .
. . :
~(~384~
: multiplexed phase-correction signal having a low frequency ; and having a phase so related linearly ~nd sequentially to the phase corrections that esch phase correction appears a~proximately simultaneously with the corresponding phase.
With standard receivers of the sequential radio-navigation system, on reception the carrier wave is filtered and demodulated in order to recover the multiplexed correction signal, and then the phase corrections contained in this ~ multiplexed correction signal are applied to the received - 10 phases so that,each phase undergoes the phase correction received at the same moment.
Such an amplitude-modulated radiogoniometric carrier wave is in general emitted by a radio beacon. '~he trans-missions of radio beacons are of different type according to , .
the field of application.
Aeronautical radio beacons have transmissions in the frequency band from 315 to 405 kHz. q'heir transmission is repetitive and of type A1 i.e. the pure carrler wave is "manipulated" for 5 seconds, that is to say, it is modulated ~, on an all-or-nothing basis by an identification code (several --letters in morse for example), and then transmission continues ,~ for 30 seconds.
Maritime radio beacons use the frequency band from , 285 to 315 kHz.
Although certain mari~ime radio beacons operate with the A1 type of transmission defined above, the great majority present trensmissions of type A2, i.e. the carrier is . ' ` . ' .
:' .
. ,, . - . . . . . ...
~0384~11 modulated in amplitude by a low-frequency signal-of fixed value which is characteristic o~ the radio beacon in the same way as the "manipulation". q'his manipulation applies for most of the time to the whole of the modulated signal, and not only the amplitude modlllation~
The duration of a transmission sequence is typically about 1 minute with the following bxeakdown:
- repetition of the identification code modulated for 15 seconds, - continuous transmission of the modulated wave for .
40 seconds, repetition of the identification code and transition for 5 seconds.
~ Certain radio beacons have a permanent transmission9 - 15 immediately resuming the cycle.
More frequently, however, the radio beacon belongs to a group of several stations, two or six for instance.
In this case the phase modulation operation defined above can be effected for a first radio beacon by a multi-plexed phase-correction signal having at least one known multiplexing segment allotted to its reference phase, that is to say, in which its phase is fixed, and so does not depend linearly on phase corrections during this known segment.
In this case the successive phase corrections are introduced in relation to this reference phase; for example, for a zero phase correction the multiplexed signal will have its refere~ce phase.
. ' :
-6- ~;
.' ' ,; .
. At ~.other radio beacon of the group the carrier : wave of the first radio beacon i.s received, demodulated and : filtered in this known segment in order to extract the reference phase therefrom. l'hereafter the same phase modu lation operation is repeated, but on the wave of the secon.d : radio beacon, and with another multiplexed phase-co.rrection signal, at the same low frequency, and adjusted to have the reference phase. :.
.~ Under these conditions, as regards the receiver of the ..
sequenti.al system of radionavigation, the operations of reception and application of phase correction can then be .- .
: - performed on any of the carrier waves emanating successively ..
.~ from different radio beacons of the group.
Advantageously, the method also includes, in the ;~
; ~5 reception of the correcti.ons, narrowband low-frequency ...
.: filtering of the correction signal or signals, the application -~ :
.~ of the phase corrections here being inhibited whenever the signal so filtered has an amplitude less than a selected value.
Preferably9 the phase-correction operation allows for .
each phase to be corrected to have a self-hold time constar.!t greater than 1 minute and, by preference, close on 10 minutes, and which is distinct from the time constant for establishing - and applying the corrections, which is preferably shorter.
.. '~he invention also provides transmitting stations and correction receivers for applying the method of the invention.
;, Other characteristics and advantages of the invention : -7-.
. . ., ~ .
103848~
will be seen on read.ing the detailed descri.ption.which follows, with reference to the accompa~ying drawi,ngs which are ~iven by way of non-restrictive example, and wherein:
~'igure 1 illustrates the electric circuitry in an application of a method embodying the invention to a radio : , beacon transmitting a manipulated standing wave, wi.th or without amplitude modul~tion;
Figure 2 illustrates generally an application of the method to A2 waves transmitted sequentially by six radio '~ 10 ~eacons respectively, of which two sla~e StatiOnG are so . synchronized in relation to a master station that these three stations can sequentially send "Differential Omega" corrections at the same carrier frequency;
~ igure ~ illustrates the electric circuitry of a . slave radio beacon embodying the invention in a sequential '. group such as'that in Figure 2;
. Figure 4 illustrates the electric circuitry of a first - type of receiver for implementing the method of the invention;
.~ Figure 5 is a timing diagram illustrating waveforms at different points of the receiver of ~igure 4;
igure 6 illustrates the electric circuitry of a second type of receiver for implementing the method of the :,, invention; and . ~ .
'. Figure 7 illustrates the electric circuitry of a third ' ~- 25 type of receiver for implementing the method of the inventionO
,_,. . :
- In the course of the present detailed description it ., ~ . .
-8- , `: ' . ~ :
- . , - - . .,. . ~ ~ , .- . :. ... ... .. . .
~ ........... .`.,. . 1 : :
.`:
10384fll `~ i5 assumed that the site selectedS in relation to which the corrections transmitted on a carrier wave are defined, co-incides approximately with the locatlon of the radio beacon transmitting this carrier wave.
q'he right-hand part of Fi~ure 1 illustrates the standard elements of an A1 or A2 standing-wave radio beacon used for radio location purposes.
Such stations contain a clock source llO, also arranged - to supply the radio beacon manipulation code, in the form of logical states corresponding, for example, to letters in Morse code. These Morse code let-ters are in-tended to be -`
intelligible to the ear of the user after detection of the radiogoniometric carrier wave. It will therefore be under-' stood that the order of magnitude of the Morse code dash and `~
dot times is between one-tenth of a seoond and 1 second.
This manipulation code is directly transmitted as an all-or-nothing modulation instruction to a circuit 112 which is the power amplifier of the radio beacon transmitter.
In the case where the radio beacon contains linear - 20 amplitude modulation, which corresponds to the A2 type, the radio beacon additionally contains a circuit 111 which is closed b,y a broken llne to represent the fact that it is ; optional. This circuit 111 produces from the clock source 110 a sinusoidal signal at selected frequency in the range 300-1000 Hz.
The output of this circuit is applied as an amplitude modulation instruction to the power amplifier 112. It is, -: :
9 ~:
- ` ` - : . . :
- 1~384~3~
of course, clear that this power amplifier will differ slightly according as the carrier wave is or is not sinu-soidally modulated in amplitude.
In a standard radio beacon the power amplifier 112 directly receives the output of a pilot frequency source (not shown) as the signal to be amplified. In accordance with the invention, the radio beacon also contains a receiver 120 of the Omega radionavigation system with its aerial 121.
This receiver is advantageously of the type which gives the highest performance, i.e. it contains a local oscillator which is synchronized to the universal time as defined by the collection of base transJnitting stations of the Omega system~
~uch a receiver notably permits circular-mode radionavigation ., in relation to a single base transmitting station of the Omega system.
However, in the present case, the receiver is fixed.
Hence it will simply give a reference phase on a 1 k~lz signa]
- synchronized to the universal time, and the received phases - relating to four of the base transmitting stations designated ; 20 in general by the subscript M and individually by the letters a, b, c and d. ~hese received phases are expressed on the ~,~! 1 kHz signal in relation to the reference phase.
~ .
In this drawing the phases are designated by the Greek letter y (small phi). This letter has the subscript M (which ~ -can assume one of the values a, b, c or d) whenever it relatesto radionavigation system waves arriving from stations having these subscripts; the subscript "ref" is applied whenever it `~
relates to the reference phase.
~ 10384~
; - All these phases, supplied individually in the form of 1 kHz signals by the Omega receiver 120, are applied to a multiplexer 122. The receiver 120 also supplies this multiplexer with signals of Omega format which locally define the time intervals in which the stations a, b, c and d respectively transmit base frequency waves to give the received phases ~ M (M = a, b, c, d) in the receiver 120.
By other means the multiplexer 122 receives phases Y'M
(phi primed) which are the theoretical phases for the base frequency and the transmitting stations a1 b, c and d ' respectively of the Omega system.
- The output of the multiplexer 122 is therefore a multi- -plexed signal at the frequency of 1 kHz; in accordance with the Omega format, its phase is linearly related to the difference between the phases ~ M which are received by the receiver 120 and the theoretical phases ~'M which are intro duced into the multiplexer 122 successively for the trans-mitting stations M = a, b, c and d.
Since the Omega system contains altogether eight base transmitting stations and only four are the object of a correction transmission (the others are often hardly per-ceptible at the site itself), several segments of the Omega format therefore remain available for the reference phase to be passed to the multiplexer 122. One of these free segments, called the reference segment, is allowed to be used for this purpose.
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~ -1~3848~
~ he multiplexed signal from the multiplexer 122 is thereupon applied to a frequency-change circuit 123 which receives a heterodyne frequency to lower the I`requency of this multiplexed signal to 20 Hz. The resulting 20 Hz signal 50 obtained is thus a low-frequency multiplexed phase-correction signal with a phase linearly related successively to the phase corrections.
~ he heterodyne frequency which can be at 980 or 1020 Hz, is supplied by a pilot frequency source 124 or, better still, from the Omega receiver itself, as will be seen from ~igure ~.
q'he pilot frequency source 12~ by other means supplies ~ the radio beacon carrier frequency which is applied to the -~ linear phase modulator 125 that receives the multiplexed signal at 20 Hz as a phase modulation input.
- 15 The output of the phase modulator 125 is applied as a -~
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signal to be amplified to the power amplifier 112 of the radio beacon transmitter which is itself coupled to an aerial --113.
I'hus the aerial 113 radiates a carrier wave which is modulated in amplitude possibly in an all-or-nothing mode by a Morse alphabet manipulation and possibly by a linear ampli-- tude modulation according to a sinusoidal frequency. This ; amplitude modulation defines the identity of the radio beacon.
In accordance with the invention, this carrier wave is also modulated in phase by the 20 Hz multiplexed phase-correction signal with a modulation index preferably less than or equal to 0.6. q'his 20 Hz signal can be regarded as a sub-carrier, :
~03~
` itself modulated in phase in multiplexed fashion.
More detailed examples of the embodiment of the circuits of Figure 1 of the present patent application appear in Canadian Patent 983,608 entitled "Method of and Apparatus for Transmitting Phase Corrections, in particular for the Omega Radionavigation System".
The receiver 120 of the present device can be the .. ~
- receiver 1 of Figure 1 of the above patent; the multi-plexer 122 contains the circuit 21 and 22 of the above patent, and the frequency-change circuit 123 includes ,4, the circuit 23 and 24 of the above patent. Finally, a simple example of the linear phase modulator 125 is constituted by the circuit 125 appearing in Figures 1 and 3 o~ the above patent.
In addition to this, in Figure 1 of the present patent application the clock 110 is synchronized from the stable internal reference of the Omega receiver 120, which is itself synchronized to the universal time defined by the base Omega transmitting stations. This synchronization is effected every 10 seconds in the form of a 'mark'.
This enables the radio beacon manipulation code to be best set in relation to the se~uence of base transmissions of the Omega system.
. ~ .,.
' :
, ~ 10384~1 Figure 2 shows a group of si~ radio beacon trans-mitting stations numbered in Xoman numerals I to VI.
Normally, these stations sequentially transmit a carrier w~ve at the same frequency with amplitude modulation of type A2. In accordance with the invention, one of the stations, say station I, is-constructed i~ the manner shown in Figure 1, except that it additionally contains a sequence clock which enables it to transmit in it-s turn. The part of this station which corresponds to the left of Figure 1 and :
which can be called the "Omega receiver and coder-modulator", ;
.;. . . . :
is designated as 210. Here the circuit 211 represents the part of tllis station which corresponds to the right-hand .. .
side of ~igure 1, together with the sequence clock~ This part can be called the radio beacon and Omega transmitting station. This station acts as a "Master" since it defines the general reference for the phase of the 20 Hz signal for the other stations of the group~ ~his reference phase of the 20 Hz signal is in fact produced in circuit 210. -The stations II, IV and Vl contain radio beacon transmitters only, desi~nated as 22, 24 and 26 respectively.
The stations III and V, like station I, contain an "Omega receiver and coder-modulator" 230 and 240 respectively, ;~
as well as a radio beacon and Omega transmitter 231 or 241 respectively. In addition to this, they contain a receiver 232 or 242 respectively for synchronization to the reference phase of the 20 Hz sub-carrier signal.
The station I therefore plays the role of Master, and ; :
: 10384~31 .
.it can be identical to the station of I~`igure 1, except for the "frequency clock" circuit which is additionally presert and is also to be found in the slave stations. '~he slave stations III and V are slightly more complicated, and so station III will now be described with refereIlce to Figure 3r On the extrene ri~ht-hand si.de Figure 3 contains the circuits 310, 311 an~ 312 and an aerial 313 which are analogous to the circui.ts 110 to 113 in Fi~lre 1.
Although the connections are not shown, the mani-pu]ation clock 310 is syncbronized from an Omega receiver 3200 . ~his synchronization is preferably effected via the .
!, sequence clock 314 which receives a mark every 10 seconds in universal time from the Omega receiver 320 along a line which ~ :
is also not shown. The sequence clock 314 defines the minute of universal time devoted to the relevant transmitting station ~- ;
and it influences the power amplifier 312 simi.larly to the manipulation clock 310 for all-or-nothing control of trans-.. . . .
mlsslon .
~he Omega receiver 320 can be identical to the receiver numbered 120 in ~igure 1.
The multiplexer 322 corresponds to the multiplexer 122, - but more details are shown since the dephasers such as 3221 which respond to the theoretical phases, are indicated.
Likewise the multiplex switches are shown, these being controlled by Omega format signals (M = 1, b, c, d, ref).
The frequency-changer 323 in ~igure 3 receives the output signal of a synthesis circuit 3235 to produce a 1020 Hz . ~
: ' ' ', : . ~
~ lQ38481 frequency from the 1000 Hz frequency arriving along the reference path from the Ome~a receiver 320.
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The output of the frequency-changer 323 is applied to the phase modulator 325 via a dephaser 326. This phase ~ 5 modulator receives the station carrier frequency from a pilot - frequency source 324. -In ~igure 3 are shown some circuits within boxes drawn by dashed lines. ~1hese circuits are present in the slave ;;
stations, but not in the master station. In other words, the electric circuitry of the master station is obtainable by , eliminating from l~igure 3 those parts which are closed by the short dashes. In this case, one must of course reconstitute a direct connection between the mixer 323 and the phase modulator 325.
In a slave station the circuit 331 is the subcarrier , synchronization receiver. It receives the multiplexed phase-correction signal like any ordinary correction-receiver, for example, the one which is described later with regard to Figure 6. However it only supplies output signals during the reference segment defined above and provided by the Omega receiver 320. '~he output of the synchronization receiver 331 is therefore constituted during the reference segment by a pure 20 Hz frequency with approximately the reference phase of the 20 Hz subcarrier signal used in the master station.
The dephaser 326 is of phase-shift memory type~ Its phase-shift instruction is effected by a phase control ampli-fier 327 which responds to its phase difference input only ~
~.
-16- ~
,' .. . .. . .
:,, . . .. . ~ , ,, , -` 10384~1 during the reference segment which is applied to it as an inhibit instruction.
~he phase difference input of the amplifier ~27 is received from a phase discriminator 328 which compares the phase coming from the receiver 331 with the phase which exists at the output of the dephaser 326. It will be recalled that these two signals are at the frequency of 20 Hæ~ and during . .
the reference segment the phase at the output of the dephaser 326 is the reference phase of the Omega receiver 320 of the slave station III, which can dif~er from that of the Omega ;~ receiver corresponding to the master station I, this latter ;~ reference phase appearing just at the output of the receiver 331.
'~hus the phase discriminator 328 will apply the ~` 15 difference between these two reference phases to the control amplifier 327 which controls the dephaser ~2h to nullify this difference.
In this way the phases of the 20 Hz signals tend to be equalized for the radio beacons I, III and V. In effect, the reference phases will be the same and, of course, the slope factor of the linear function relating the phase corrections to the phase of the multiplexed correction - signal wlll be the same for all these stations.
Moreover the Omega receivers such as 320 in the radio ~ 25 beacons have pilot-frequency sources of very high quality, - and so the phase deviation of the 20 Hz frequency between two receivers of this kind is small. Hence the control .
-17 ~
~: .
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` ~ 10384~11 action constituted by the circuits ~2~ and 328 during the reference segment will not have to be very strong to compensate for this phase deviation.
'i Variou~ means of reception of "~ifferential Vmega"
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phase corrections and of application of these corrections in a base Omega xeceiver will now be described.
For greater clarity, in ~'igures 4, 6 and 7 a hori-zontal chain-dotted line has been drawn to sepaxate the Omega receiver from the correction receiver, the Omega receiver being below the line. The separation cannot ho~lever be total, in fact, since the corrections provided by the correction receiver are applied to the received phases obtained in the ;~
` Omega receiver. `
In Figure 4 the reception and application of the phase corrections are of a first type, according to which the multi plexed phase-correction signal is regenerated in the correction .~ .
receiver and directly applied without demultiplexing to the signal derived in the Omega receiver for waves received at ~. :
the base frequency of the radionavigation system. ~his i5 -.
; 20 made possible by the fact that the format of the multiplexed phase-correction signals at the 20 Hz subcarrier frequency is the same as the transmission format of the Omega system at the base frequency.
More precisely, Figure 4 contains a receiver stage 410 for reception and filtering of the carrier wave, changing its frequency and amplifying it. The output of the reception ;~
stage 410 is applied to the phase discrimina~or 411. ~he ~-.-, .
~ .0384~1 output of this discriminator 411 is the ~ultiplexed phase-correction signal at 20 Hz which contains the phase corrections ~ ~ M = ~'M ~ Y M for four base tr~msmittiIlg stations for which M = a, b, c and d. This signal also contains the reference phase ~ ref which can be used for circular-mode radionavigation, as described with reference to Figure 3, and which ~ill not be considered in the following description of the receivers.
The corrections are then applied to a 20 Hz filter which has two separate identical OUtplltS for reasons of adaptation which experts will understand.
The Omega receiver of Figure 4 contai~s a low-frequency amplifier 420 with filtering and, possibly, a frequency change.
The output of this amplifier 420 is therefore a signal of frequency f having phases y M~ where sequentially M = a, b, c, d. ~his signal is illustrated as a function of time by the line L1 in ~igure 5.
'The line L2 of ~igure 5 shows the output signal of the filter 412, with the exception of the reference phase.
'~hese two signals are mixed in a frequency-change circuit 421, the output of which is represented by the line L3 in ~igure 5. 'The frequency produced is f ~ 20 Hz, and the phase is equal to the sum total of each received phase y M
represented by line L1 and of each corresponding phase correc-tion /\ ~ M represented by the line L2.
.. . .
~he corrected phases so obtained are applied to an _~9_ s amplifier 422 at the intermediate frequerlcy f ~ 20 Hz, followed by the demlultiplexer 42~ supplying four channels 424a to 424d.
.: , - q'hese four channels 424 deduce the phase data from the demultiplexed corrected signals.
... .
In each channel 424 a capacitor has been shown in order to illustrate the fact that these channels possess a :
memor;y function, i.e. a large self-hold time constant.
This time const~nt is advantageously greater than 1 minute, and preferably close on 10 minutes.
By other means, the second output of filter 412 i5 coupled to a circuit 415 which is an amplitude threshold detector, which produces an output signal whenevex the amplitude of the multiplexed phase-correction signal, or 20 Hz subcarrier, becomes less than a selected value. Its output is connected to a trip or trigger which in this case simultaneously controls the demultiplexer 423 and an alarm `
circuit 418 which is itself coupled to a read-out permissive circuit, the read-out being performed by the intermediary of switches 425a to 425d which are placed downstream from the channels 424.
:., , . - :
~hus, when the 20 Hz sig~lal becomes insufficient in -~ -amplitude, the demultiplexing is inhibited, and the read-out is forbidden, signifying that the switches upstream from channels 424 (not shown, but included in the demultiplexer 423) and downstream from channels 424 (switches 425) remain open.
.. .. .
1~38~8 1 In consequence these channels exercise their memory function without upstream perturbation by false data, and without any downstream withdrawal for read-out alterinq their constant.
This is an important characteristic of the device, for the detector 415 goes to perform its function at every disappearance of the carrier wave, whether this may be by reason of the manipulation, or because of the sequential functioning whenever it is a question of a group of radio beacons such as the group in Figure 2.
Some more detailed form of certain circuits of the - present Figure 4 are described with reference to Figure 5 in ; the abovementioned patent. In particular, the present receiver 410 corresponds to the elements 51, 52, 53, 521 ;j and 531 of the referenced patent, but with the values of the intermediate frequencies here being adjusted for correspondence with the frequency band of the radio beacons.
Similarly, the discriminator 411 and the filter 412 corres-pond to the elements 541 and 542 of the cited patent.
In the other two types of receiver shown in Figures 6 and 7 the phase-correction data are converted into analogue form before being applied to the received phases. In the receiver of Figure 6 the received-phase signals are dephased .~ before multiplexing in accordance with the analogue phase-correction data. In the receiver of Figure 7 the phase-correction data are individually added to the received-phase data, converted into a convenient form for use.
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10384~ ~
Fi~ures 6 and 7 otherwise have in common the elements shown at the top of these figures, namely the corrcction receiver, discriminator, 20 Hz filter, amplitude threshold ; detector and trigger. ~hese elements correspond otherwise to those in Figure 4, and they have the same r~eference number, except for the digit representing the hundreds, which stands for the number of the figure in each hlstance~
In Figure 6 the 20 ~z multiplexed phase-correction signal is applied to a demultiplexer 613 which receives the Omega format signals as a multiplexing instruction. '~he demultiplexer 613 is inhibited by the output of trigger 616 whenever the multiplexed signal amplitude passes below the threshold.
'~he outputs of the demultiplexer 613 are applied to a . , .
- 15 plurality of synchronous filters 614a to 614d. Each of these synchronous f-ilters contains a narrowband filter and a synchronous demodulator at 20 Hz which is controlled during the phase correction of the multiplexing segment to which it is allotted.
Such elements further contain a capacitor in their output stage, and so they are capable of the memory function with a time constant of the same order as that described ; with reference to ~igure 4. In actual fact, they also very often contain a veritable "phase memory".
In Figure 6 the Omega receiver supplies, for instance, received phases y M which are carried by a frequency of 1 ~z.
These phases are multiplexed due to the fact that they are 10384~
received at the same base frequency of the Gmega system.
They are applied to a multiplexed dephaser 621 which by other means receives the Omega segments and the synchronous phase-corrections 614 for application of each phase correction during the corresponding segment.
The output of the multiplexed dephaser 621 therefore - transmits signals which are at the frequency of 1 kMz and are corrected in phase. These signals are applied to a processing circuit 622, followed by a demultiplexer 623 and the channels 624a to 624_, these being standard circuits in an Omega receiver such as the one sold with the commercial -~
~ designation "NRNX lA" or "M2A" by S E R C E L.*
: Each synchronous filter 614 can contain the elements ~-~
-, ' 55 which are described by reference to Figure 6 in the above-mentioned patent, having regard to the fact that these elements also embody the demultiplexing function of the .` '~
circuit 613 of the present device.
The multiplexed dephaser 621 contains, for example, .,;
a fast-response dephaser, the phase shift instruction of which is multiplexed along the paths a, b, c, d.
For the third type of receiver, Figure 7 contains some elements which are analogous to those of Figure 6, namely, .~ the demultiplexer 713 and the synchronous filters 714_ to ;
714d.
The Omega reception part of Figure 7 contains a receiver circuit 727 with amplification, filtering and frequency-changing, followed by a demultiplexer 721, then by channels *Trademark for the Societe d'Etudes, Recherches et Constructions Electroniques ~'1, .
:
- . . E~. -~,: , . ' ' . ' ' ' ' 10384~3L :
722a to 722d in order to obtain received-phase data in a form which can be used directly.
In the t~e of receiver of Figure 7 the phase-correction data coming from the channels 714 is combined with the received-phase data arriving from the channels 722 in - the dephasers 723a to 72~. If the received phases from the ; channels 722 are carried by a frequency of ~ kHz~ then the circuits 723 are effective dephasers for this frequency.
If ~he received phases as well as the phase corrections are in analogue form, the circuits 723 can be analogue sub-tractors.
Clearly, in the embodiments illustrated in Figures 6 and 7 the action of the amplitude threshold detector and of the trigger is very important in enabling the memory function of the synchronous filters to play its role whenever the -~
carrier wave vanishes because of manipulation or, more parti~
cularly, because of sequential operation. The difference vis-à-vis Figure 4 resides in the fact that the read-out can be permanent in the receivers of Figures 6 and 7, the ; 20 frequeney controls contained in the narrowband synchronous filters here having a phase memory.
Experiments performed by the Applicant have shown that goniometric use of the carrier wave phase modulated by phase corrections in accordance with the invention is not affected by this phase modulation. This is true equally as well when the radiogoniometry is carried out with a moving-eoil receiver as when with more complicated receivers using -24~
. ~ ' .
- ~03848~L
a comparison between the wave received by a whip aerial "of reference" and the wave received by fixed crossed loops.
- However, the phase modulation can have a sli.ght influence on the intelliKibility of the i~entification signa]s . 5 of certain types of radio beacons.
: In particular, in aeronautical radio beacons with A1 type modulation the receivers generally use a beat frequ.ency :, osci].lator (B.F.O.) and the manipulation becomes evident by detectlon of the beat sig~al. In this case the effect of -~ 10 phase modulation in accordance with the invention will be perceptible in the form of a slight "vibrato" which cannot ~-nevertheless seriously affect the intelligibility of mani-,: , - pulated identification signals.
., , The studies and experiments of the ~pplicant ~elate .:; 15 especially to the possible influence of the modulation and manipulation characteristics necessary for operation of the radio beacon on the satisfactory functioning of "Differential ;~ Omega" correction receivers embodying the invention.
. Standard use of limiters upstream from the phase discriminator and careful filtering in the reception stages, properly speaking, already has the effect of sufficiently attenuating linear amplitude modulation whenever it exists.
In the event of intermodulations their effect on the correction carrier signals is further limited by reason of very effective filterlng of the multiplexed correction signal at 20 Hz and also in the subsequent synchronous demodu-lators, at least for the receivers of Figures 6 and 7.
.. .. . .. .. . .. .
. .
: ~
384~1 As regards the all-or-nothing modulation due to the ~ manipulation, the first experiments of the ~pplicant have `- shown that it has practically no perceptible effect on thè
transmission of "Differential Omega" corrections embodying the invention.
By contrast, the Applicant has paid particular atten-tion to defects which can be caused by periodical interruption of transmis~ion when only some of the radio beacons of a group are equipped for "Differential Omega" transmission, as is the case in ~igure 2. It will be considered that the ; -time allotted to each station is 1 minute, the period, or overall sequence time, here being 6 minutes.
Under these conditions the best result which may be obtainable duringr the "silences" of the transmission consists in keeping intact the correction values obtained during the most recent transmission in order to apply them throughout the interruption period due to these silences.
In fact, however, the correction values which should be applied, can vary significantly, whereas it is a constant value which is preserved.
The following Table gives some values observed by the .
Applicant for phase root mean-square errors expressed as a -percentage in turn for standing transmission or for various -cases of se~uential transmission.
The first row of the Table relates to approximate values associated only with the mode of transmission of the corrections in accordance with the invention, whilst the -26- ~-`.
- : .. , ., ~ . ... : , ~ 103848~L
~ second. row concerns the total error, allowing for the : fact that the corrections obtained at the selected site are not completely correlated with the corrections which should be made in all the zone where the~ are applied.
.~ 5 r~he root-mean-square error due to this decorrelation is generally evaluated to be about 1.5 percent when the . distance from the correction transmittlng station to the user is 300 km.
r~he th.ird row of the Table represents the degradation : 10 coefficient referred to sequential operation~ r~here is a ' slight degradation in standing transmission due to the fact . .
~ that the transmission is never perfect.
~ .
. . _ . . . ._ ._ .
:: . Standing Sequential Sequential, . transmission 1' on 2' period 3' .. . ._ . . ... :. _ _ 1' on 3' .
Root-mean-square deviation 0.216 1.04 2.15 .
... .. ... ... .. . _ ._ Root-mean-square error 1.51 1.83 2.62 ... __._ . .... _ . _ . . . . ~
Degradation .
coefficient 1.01 1.22 1.7 ~- .
It appears that standing transmission of "Differential Omega" corrections permits a 1:5 improvement in accuracy compared with the tabulated corrections defined by the Ame~iccm organization U.~. Naval Oceanographic Office. It is therefore clear that the values given in the above r~able for the two sequential modes of operation correspond also to distinctly better results than the tabulated corrections mentioned.
. ' ' ,10384~
This holds good for a range of 300 km from the selected site; beyond this range, it is preferable to use another correction transmitting station or to revert to the tabulated corrections.
. . .
... i ~, .
~ 5 For this purpose it is advantageous to use, jointly .. ..
- with a method embodying the present invention, the method ~
described in the French Patent 2,224,929, entitled ; -"Dispositif de correction de phase, notamment pour un recepteur de radionavigation Omega" (Phase correction device, notably for an Omega radionavigation receiver). The two .
, means can be used alternately, the corrections arriving from ~~ one or the other, or simultaneously, in which case the - corrections originating from the two means are then applied by two dephasers mounted in series to the phases received by the base Omega receiver. -; In this latter case, the correction device of the I ~ :
last-mentioned patent is not used for memory-storage of the U.S.N.O.O. tabulated corrections directly, but to contain differential values. These differential values are obtained by deducting the tabulated values relating to the site selected for measuring the "Differential Omega" ;
corrections transmitted and used, from the values of the - U.S.N.O.O. tabulated corrections for the location of the receiver.
~ ' ' ' :
,.
.' .
''' '~"
. . -: . ,
It is known that the differential-mode use of a radio-navigation system presumes supplementary transmission of phase corrections defined by the difference between each phase .,.: .
10 received at a selected site and the corresponding theoretical phase. The theoretical phase at a point is that which, in the - theoretical network of position lines, satisfies a reciprocal and stationary correspondence with the geographical position of this point. ~he received phase varies complexly with time 15 in relation to the theoretica1 phase, and this produces untimely errors in this reciprocal correspondence. It is therefore apparent that the knowledge of the corrections thus transmitted permits substantial reduction of these untimely errors.
This differential usage applies only in a certain zone -~
.
close to the selected site. It is therefore desirable that the supplementary transmission should be extended to this zone, whatever type of receivers of the sequential radio-navigation system are to be found there.
For the same reason, a large number of supplementary transmissions of this kind also need to be provided if the differential-mode radionavigation system is desired for use _ _ . , :, 10384fll over long distances. In particular, in coastal areas the supplementary phase-correction transmissions should be made in sufficient number to enable the differential-mode radio-navi~ation system to be used along all coast and thereby obtain the advantage of greater precision.
The radionavigation system receivers intended for additionally receiving this correction transmission can, for their part, range from the ordinary type to the highest degree of precision according to the application. Also it is ... . .
clearly necessary for the same correction receiver to be usable over great distances for a full set of these supple-mentary transmissions and without involving the user in -complicated operations. In other words, an intervening normalization is required over the set of supplementary phase correction transmissions. -Each correction transmitting station has therefore to allow general diffusion over a certain zone for receivers which range from the ordinary t~pe to the greatest precision, more generally, a large number of such transmitting stations have to satisfy this criterion, while at the same time permitting a normalization of utilization and great precision.
In the case of the Omega system, for example, eight base transmitting stations are provided to cover all the globe, the distance between transmitting stations here being of the order of 8000 km (5000 miles).
According to present estimates, the utilization range ; of one correction transmittinD station will at most be several -- , : ~, .............................................. .
. ~
~ , .. . ... . .. ~ .
1 hundred kilometers. It is therefore clear that a considerable number of correction transmitting stations is required.
Having regard to the present congestion of the ether, frequency allocations are becoming increasingly more difficult . .
to obtain for differential radionavigation, even with ~ technical requirements as fundamental as those which have ;~ just been presented.
In the future it seems unlikely that the allocation of new radio channels will be sufficient to solve this problem, for it will probably be necessary to install progressively more and more correction transmitting stations, and this will quickly saturate these new channels.
Moreover it is clear that most of the channels already occupied are not compatible with all the requirements set out above for the supplementary transmission of corrections, namely, diffusion over predetermined zones, great simplicity or utilization, normalization over a large number of different transmissions and high precision.
However the present invention contributes a parti-cularly satisfying solution to the problem thus posed.
According to the invention, a method of aid to navi-gation is provided for use in differential mode in a sequential system of radionavigation by phase reception.
In transmission, a radiogoniometric carrier wave - amplitude modulated as an identification code, is modulated in phase or frequency by a .
. . :
~(~384~
: multiplexed phase-correction signal having a low frequency ; and having a phase so related linearly ~nd sequentially to the phase corrections that esch phase correction appears a~proximately simultaneously with the corresponding phase.
With standard receivers of the sequential radio-navigation system, on reception the carrier wave is filtered and demodulated in order to recover the multiplexed correction signal, and then the phase corrections contained in this ~ multiplexed correction signal are applied to the received - 10 phases so that,each phase undergoes the phase correction received at the same moment.
Such an amplitude-modulated radiogoniometric carrier wave is in general emitted by a radio beacon. '~he trans-missions of radio beacons are of different type according to , .
the field of application.
Aeronautical radio beacons have transmissions in the frequency band from 315 to 405 kHz. q'heir transmission is repetitive and of type A1 i.e. the pure carrler wave is "manipulated" for 5 seconds, that is to say, it is modulated ~, on an all-or-nothing basis by an identification code (several --letters in morse for example), and then transmission continues ,~ for 30 seconds.
Maritime radio beacons use the frequency band from , 285 to 315 kHz.
Although certain mari~ime radio beacons operate with the A1 type of transmission defined above, the great majority present trensmissions of type A2, i.e. the carrier is . ' ` . ' .
:' .
. ,, . - . . . . . ...
~0384~11 modulated in amplitude by a low-frequency signal-of fixed value which is characteristic o~ the radio beacon in the same way as the "manipulation". q'his manipulation applies for most of the time to the whole of the modulated signal, and not only the amplitude modlllation~
The duration of a transmission sequence is typically about 1 minute with the following bxeakdown:
- repetition of the identification code modulated for 15 seconds, - continuous transmission of the modulated wave for .
40 seconds, repetition of the identification code and transition for 5 seconds.
~ Certain radio beacons have a permanent transmission9 - 15 immediately resuming the cycle.
More frequently, however, the radio beacon belongs to a group of several stations, two or six for instance.
In this case the phase modulation operation defined above can be effected for a first radio beacon by a multi-plexed phase-correction signal having at least one known multiplexing segment allotted to its reference phase, that is to say, in which its phase is fixed, and so does not depend linearly on phase corrections during this known segment.
In this case the successive phase corrections are introduced in relation to this reference phase; for example, for a zero phase correction the multiplexed signal will have its refere~ce phase.
. ' :
-6- ~;
.' ' ,; .
. At ~.other radio beacon of the group the carrier : wave of the first radio beacon i.s received, demodulated and : filtered in this known segment in order to extract the reference phase therefrom. l'hereafter the same phase modu lation operation is repeated, but on the wave of the secon.d : radio beacon, and with another multiplexed phase-co.rrection signal, at the same low frequency, and adjusted to have the reference phase. :.
.~ Under these conditions, as regards the receiver of the ..
sequenti.al system of radionavigation, the operations of reception and application of phase correction can then be .- .
: - performed on any of the carrier waves emanating successively ..
.~ from different radio beacons of the group.
Advantageously, the method also includes, in the ;~
; ~5 reception of the correcti.ons, narrowband low-frequency ...
.: filtering of the correction signal or signals, the application -~ :
.~ of the phase corrections here being inhibited whenever the signal so filtered has an amplitude less than a selected value.
Preferably9 the phase-correction operation allows for .
each phase to be corrected to have a self-hold time constar.!t greater than 1 minute and, by preference, close on 10 minutes, and which is distinct from the time constant for establishing - and applying the corrections, which is preferably shorter.
.. '~he invention also provides transmitting stations and correction receivers for applying the method of the invention.
;, Other characteristics and advantages of the invention : -7-.
. . ., ~ .
103848~
will be seen on read.ing the detailed descri.ption.which follows, with reference to the accompa~ying drawi,ngs which are ~iven by way of non-restrictive example, and wherein:
~'igure 1 illustrates the electric circuitry in an application of a method embodying the invention to a radio : , beacon transmitting a manipulated standing wave, wi.th or without amplitude modul~tion;
Figure 2 illustrates generally an application of the method to A2 waves transmitted sequentially by six radio '~ 10 ~eacons respectively, of which two sla~e StatiOnG are so . synchronized in relation to a master station that these three stations can sequentially send "Differential Omega" corrections at the same carrier frequency;
~ igure ~ illustrates the electric circuitry of a . slave radio beacon embodying the invention in a sequential '. group such as'that in Figure 2;
. Figure 4 illustrates the electric circuitry of a first - type of receiver for implementing the method of the invention;
.~ Figure 5 is a timing diagram illustrating waveforms at different points of the receiver of ~igure 4;
igure 6 illustrates the electric circuitry of a second type of receiver for implementing the method of the :,, invention; and . ~ .
'. Figure 7 illustrates the electric circuitry of a third ' ~- 25 type of receiver for implementing the method of the inventionO
,_,. . :
- In the course of the present detailed description it ., ~ . .
-8- , `: ' . ~ :
- . , - - . .,. . ~ ~ , .- . :. ... ... .. . .
~ ........... .`.,. . 1 : :
.`:
10384fll `~ i5 assumed that the site selectedS in relation to which the corrections transmitted on a carrier wave are defined, co-incides approximately with the locatlon of the radio beacon transmitting this carrier wave.
q'he right-hand part of Fi~ure 1 illustrates the standard elements of an A1 or A2 standing-wave radio beacon used for radio location purposes.
Such stations contain a clock source llO, also arranged - to supply the radio beacon manipulation code, in the form of logical states corresponding, for example, to letters in Morse code. These Morse code let-ters are in-tended to be -`
intelligible to the ear of the user after detection of the radiogoniometric carrier wave. It will therefore be under-' stood that the order of magnitude of the Morse code dash and `~
dot times is between one-tenth of a seoond and 1 second.
This manipulation code is directly transmitted as an all-or-nothing modulation instruction to a circuit 112 which is the power amplifier of the radio beacon transmitter.
In the case where the radio beacon contains linear - 20 amplitude modulation, which corresponds to the A2 type, the radio beacon additionally contains a circuit 111 which is closed b,y a broken llne to represent the fact that it is ; optional. This circuit 111 produces from the clock source 110 a sinusoidal signal at selected frequency in the range 300-1000 Hz.
The output of this circuit is applied as an amplitude modulation instruction to the power amplifier 112. It is, -: :
9 ~:
- ` ` - : . . :
- 1~384~3~
of course, clear that this power amplifier will differ slightly according as the carrier wave is or is not sinu-soidally modulated in amplitude.
In a standard radio beacon the power amplifier 112 directly receives the output of a pilot frequency source (not shown) as the signal to be amplified. In accordance with the invention, the radio beacon also contains a receiver 120 of the Omega radionavigation system with its aerial 121.
This receiver is advantageously of the type which gives the highest performance, i.e. it contains a local oscillator which is synchronized to the universal time as defined by the collection of base transJnitting stations of the Omega system~
~uch a receiver notably permits circular-mode radionavigation ., in relation to a single base transmitting station of the Omega system.
However, in the present case, the receiver is fixed.
Hence it will simply give a reference phase on a 1 k~lz signa]
- synchronized to the universal time, and the received phases - relating to four of the base transmitting stations designated ; 20 in general by the subscript M and individually by the letters a, b, c and d. ~hese received phases are expressed on the ~,~! 1 kHz signal in relation to the reference phase.
~ .
In this drawing the phases are designated by the Greek letter y (small phi). This letter has the subscript M (which ~ -can assume one of the values a, b, c or d) whenever it relatesto radionavigation system waves arriving from stations having these subscripts; the subscript "ref" is applied whenever it `~
relates to the reference phase.
~ 10384~
; - All these phases, supplied individually in the form of 1 kHz signals by the Omega receiver 120, are applied to a multiplexer 122. The receiver 120 also supplies this multiplexer with signals of Omega format which locally define the time intervals in which the stations a, b, c and d respectively transmit base frequency waves to give the received phases ~ M (M = a, b, c, d) in the receiver 120.
By other means the multiplexer 122 receives phases Y'M
(phi primed) which are the theoretical phases for the base frequency and the transmitting stations a1 b, c and d ' respectively of the Omega system.
- The output of the multiplexer 122 is therefore a multi- -plexed signal at the frequency of 1 kHz; in accordance with the Omega format, its phase is linearly related to the difference between the phases ~ M which are received by the receiver 120 and the theoretical phases ~'M which are intro duced into the multiplexer 122 successively for the trans-mitting stations M = a, b, c and d.
Since the Omega system contains altogether eight base transmitting stations and only four are the object of a correction transmission (the others are often hardly per-ceptible at the site itself), several segments of the Omega format therefore remain available for the reference phase to be passed to the multiplexer 122. One of these free segments, called the reference segment, is allowed to be used for this purpose.
.
~ -1~3848~
~ he multiplexed signal from the multiplexer 122 is thereupon applied to a frequency-change circuit 123 which receives a heterodyne frequency to lower the I`requency of this multiplexed signal to 20 Hz. The resulting 20 Hz signal 50 obtained is thus a low-frequency multiplexed phase-correction signal with a phase linearly related successively to the phase corrections.
~ he heterodyne frequency which can be at 980 or 1020 Hz, is supplied by a pilot frequency source 124 or, better still, from the Omega receiver itself, as will be seen from ~igure ~.
q'he pilot frequency source 12~ by other means supplies ~ the radio beacon carrier frequency which is applied to the -~ linear phase modulator 125 that receives the multiplexed signal at 20 Hz as a phase modulation input.
- 15 The output of the phase modulator 125 is applied as a -~
.
signal to be amplified to the power amplifier 112 of the radio beacon transmitter which is itself coupled to an aerial --113.
I'hus the aerial 113 radiates a carrier wave which is modulated in amplitude possibly in an all-or-nothing mode by a Morse alphabet manipulation and possibly by a linear ampli-- tude modulation according to a sinusoidal frequency. This ; amplitude modulation defines the identity of the radio beacon.
In accordance with the invention, this carrier wave is also modulated in phase by the 20 Hz multiplexed phase-correction signal with a modulation index preferably less than or equal to 0.6. q'his 20 Hz signal can be regarded as a sub-carrier, :
~03~
` itself modulated in phase in multiplexed fashion.
More detailed examples of the embodiment of the circuits of Figure 1 of the present patent application appear in Canadian Patent 983,608 entitled "Method of and Apparatus for Transmitting Phase Corrections, in particular for the Omega Radionavigation System".
The receiver 120 of the present device can be the .. ~
- receiver 1 of Figure 1 of the above patent; the multi-plexer 122 contains the circuit 21 and 22 of the above patent, and the frequency-change circuit 123 includes ,4, the circuit 23 and 24 of the above patent. Finally, a simple example of the linear phase modulator 125 is constituted by the circuit 125 appearing in Figures 1 and 3 o~ the above patent.
In addition to this, in Figure 1 of the present patent application the clock 110 is synchronized from the stable internal reference of the Omega receiver 120, which is itself synchronized to the universal time defined by the base Omega transmitting stations. This synchronization is effected every 10 seconds in the form of a 'mark'.
This enables the radio beacon manipulation code to be best set in relation to the se~uence of base transmissions of the Omega system.
. ~ .,.
' :
, ~ 10384~1 Figure 2 shows a group of si~ radio beacon trans-mitting stations numbered in Xoman numerals I to VI.
Normally, these stations sequentially transmit a carrier w~ve at the same frequency with amplitude modulation of type A2. In accordance with the invention, one of the stations, say station I, is-constructed i~ the manner shown in Figure 1, except that it additionally contains a sequence clock which enables it to transmit in it-s turn. The part of this station which corresponds to the left of Figure 1 and :
which can be called the "Omega receiver and coder-modulator", ;
.;. . . . :
is designated as 210. Here the circuit 211 represents the part of tllis station which corresponds to the right-hand .. .
side of ~igure 1, together with the sequence clock~ This part can be called the radio beacon and Omega transmitting station. This station acts as a "Master" since it defines the general reference for the phase of the 20 Hz signal for the other stations of the group~ ~his reference phase of the 20 Hz signal is in fact produced in circuit 210. -The stations II, IV and Vl contain radio beacon transmitters only, desi~nated as 22, 24 and 26 respectively.
The stations III and V, like station I, contain an "Omega receiver and coder-modulator" 230 and 240 respectively, ;~
as well as a radio beacon and Omega transmitter 231 or 241 respectively. In addition to this, they contain a receiver 232 or 242 respectively for synchronization to the reference phase of the 20 Hz sub-carrier signal.
The station I therefore plays the role of Master, and ; :
: 10384~31 .
.it can be identical to the station of I~`igure 1, except for the "frequency clock" circuit which is additionally presert and is also to be found in the slave stations. '~he slave stations III and V are slightly more complicated, and so station III will now be described with refereIlce to Figure 3r On the extrene ri~ht-hand si.de Figure 3 contains the circuits 310, 311 an~ 312 and an aerial 313 which are analogous to the circui.ts 110 to 113 in Fi~lre 1.
Although the connections are not shown, the mani-pu]ation clock 310 is syncbronized from an Omega receiver 3200 . ~his synchronization is preferably effected via the .
!, sequence clock 314 which receives a mark every 10 seconds in universal time from the Omega receiver 320 along a line which ~ :
is also not shown. The sequence clock 314 defines the minute of universal time devoted to the relevant transmitting station ~- ;
and it influences the power amplifier 312 simi.larly to the manipulation clock 310 for all-or-nothing control of trans-.. . . .
mlsslon .
~he Omega receiver 320 can be identical to the receiver numbered 120 in ~igure 1.
The multiplexer 322 corresponds to the multiplexer 122, - but more details are shown since the dephasers such as 3221 which respond to the theoretical phases, are indicated.
Likewise the multiplex switches are shown, these being controlled by Omega format signals (M = 1, b, c, d, ref).
The frequency-changer 323 in ~igure 3 receives the output signal of a synthesis circuit 3235 to produce a 1020 Hz . ~
: ' ' ', : . ~
~ lQ38481 frequency from the 1000 Hz frequency arriving along the reference path from the Ome~a receiver 320.
. .
The output of the frequency-changer 323 is applied to the phase modulator 325 via a dephaser 326. This phase ~ 5 modulator receives the station carrier frequency from a pilot - frequency source 324. -In ~igure 3 are shown some circuits within boxes drawn by dashed lines. ~1hese circuits are present in the slave ;;
stations, but not in the master station. In other words, the electric circuitry of the master station is obtainable by , eliminating from l~igure 3 those parts which are closed by the short dashes. In this case, one must of course reconstitute a direct connection between the mixer 323 and the phase modulator 325.
In a slave station the circuit 331 is the subcarrier , synchronization receiver. It receives the multiplexed phase-correction signal like any ordinary correction-receiver, for example, the one which is described later with regard to Figure 6. However it only supplies output signals during the reference segment defined above and provided by the Omega receiver 320. '~he output of the synchronization receiver 331 is therefore constituted during the reference segment by a pure 20 Hz frequency with approximately the reference phase of the 20 Hz subcarrier signal used in the master station.
The dephaser 326 is of phase-shift memory type~ Its phase-shift instruction is effected by a phase control ampli-fier 327 which responds to its phase difference input only ~
~.
-16- ~
,' .. . .. . .
:,, . . .. . ~ , ,, , -` 10384~1 during the reference segment which is applied to it as an inhibit instruction.
~he phase difference input of the amplifier ~27 is received from a phase discriminator 328 which compares the phase coming from the receiver 331 with the phase which exists at the output of the dephaser 326. It will be recalled that these two signals are at the frequency of 20 Hæ~ and during . .
the reference segment the phase at the output of the dephaser 326 is the reference phase of the Omega receiver 320 of the slave station III, which can dif~er from that of the Omega ;~ receiver corresponding to the master station I, this latter ;~ reference phase appearing just at the output of the receiver 331.
'~hus the phase discriminator 328 will apply the ~` 15 difference between these two reference phases to the control amplifier 327 which controls the dephaser ~2h to nullify this difference.
In this way the phases of the 20 Hz signals tend to be equalized for the radio beacons I, III and V. In effect, the reference phases will be the same and, of course, the slope factor of the linear function relating the phase corrections to the phase of the multiplexed correction - signal wlll be the same for all these stations.
Moreover the Omega receivers such as 320 in the radio ~ 25 beacons have pilot-frequency sources of very high quality, - and so the phase deviation of the 20 Hz frequency between two receivers of this kind is small. Hence the control .
-17 ~
~: .
.
` ~ 10384~11 action constituted by the circuits ~2~ and 328 during the reference segment will not have to be very strong to compensate for this phase deviation.
'i Variou~ means of reception of "~ifferential Vmega"
:: .
phase corrections and of application of these corrections in a base Omega xeceiver will now be described.
For greater clarity, in ~'igures 4, 6 and 7 a hori-zontal chain-dotted line has been drawn to sepaxate the Omega receiver from the correction receiver, the Omega receiver being below the line. The separation cannot ho~lever be total, in fact, since the corrections provided by the correction receiver are applied to the received phases obtained in the ;~
` Omega receiver. `
In Figure 4 the reception and application of the phase corrections are of a first type, according to which the multi plexed phase-correction signal is regenerated in the correction .~ .
receiver and directly applied without demultiplexing to the signal derived in the Omega receiver for waves received at ~. :
the base frequency of the radionavigation system. ~his i5 -.
; 20 made possible by the fact that the format of the multiplexed phase-correction signals at the 20 Hz subcarrier frequency is the same as the transmission format of the Omega system at the base frequency.
More precisely, Figure 4 contains a receiver stage 410 for reception and filtering of the carrier wave, changing its frequency and amplifying it. The output of the reception ;~
stage 410 is applied to the phase discrimina~or 411. ~he ~-.-, .
~ .0384~1 output of this discriminator 411 is the ~ultiplexed phase-correction signal at 20 Hz which contains the phase corrections ~ ~ M = ~'M ~ Y M for four base tr~msmittiIlg stations for which M = a, b, c and d. This signal also contains the reference phase ~ ref which can be used for circular-mode radionavigation, as described with reference to Figure 3, and which ~ill not be considered in the following description of the receivers.
The corrections are then applied to a 20 Hz filter which has two separate identical OUtplltS for reasons of adaptation which experts will understand.
The Omega receiver of Figure 4 contai~s a low-frequency amplifier 420 with filtering and, possibly, a frequency change.
The output of this amplifier 420 is therefore a signal of frequency f having phases y M~ where sequentially M = a, b, c, d. ~his signal is illustrated as a function of time by the line L1 in ~igure 5.
'The line L2 of ~igure 5 shows the output signal of the filter 412, with the exception of the reference phase.
'~hese two signals are mixed in a frequency-change circuit 421, the output of which is represented by the line L3 in ~igure 5. 'The frequency produced is f ~ 20 Hz, and the phase is equal to the sum total of each received phase y M
represented by line L1 and of each corresponding phase correc-tion /\ ~ M represented by the line L2.
.. . .
~he corrected phases so obtained are applied to an _~9_ s amplifier 422 at the intermediate frequerlcy f ~ 20 Hz, followed by the demlultiplexer 42~ supplying four channels 424a to 424d.
.: , - q'hese four channels 424 deduce the phase data from the demultiplexed corrected signals.
... .
In each channel 424 a capacitor has been shown in order to illustrate the fact that these channels possess a :
memor;y function, i.e. a large self-hold time constant.
This time const~nt is advantageously greater than 1 minute, and preferably close on 10 minutes.
By other means, the second output of filter 412 i5 coupled to a circuit 415 which is an amplitude threshold detector, which produces an output signal whenevex the amplitude of the multiplexed phase-correction signal, or 20 Hz subcarrier, becomes less than a selected value. Its output is connected to a trip or trigger which in this case simultaneously controls the demultiplexer 423 and an alarm `
circuit 418 which is itself coupled to a read-out permissive circuit, the read-out being performed by the intermediary of switches 425a to 425d which are placed downstream from the channels 424.
:., , . - :
~hus, when the 20 Hz sig~lal becomes insufficient in -~ -amplitude, the demultiplexing is inhibited, and the read-out is forbidden, signifying that the switches upstream from channels 424 (not shown, but included in the demultiplexer 423) and downstream from channels 424 (switches 425) remain open.
.. .. .
1~38~8 1 In consequence these channels exercise their memory function without upstream perturbation by false data, and without any downstream withdrawal for read-out alterinq their constant.
This is an important characteristic of the device, for the detector 415 goes to perform its function at every disappearance of the carrier wave, whether this may be by reason of the manipulation, or because of the sequential functioning whenever it is a question of a group of radio beacons such as the group in Figure 2.
Some more detailed form of certain circuits of the - present Figure 4 are described with reference to Figure 5 in ; the abovementioned patent. In particular, the present receiver 410 corresponds to the elements 51, 52, 53, 521 ;j and 531 of the referenced patent, but with the values of the intermediate frequencies here being adjusted for correspondence with the frequency band of the radio beacons.
Similarly, the discriminator 411 and the filter 412 corres-pond to the elements 541 and 542 of the cited patent.
In the other two types of receiver shown in Figures 6 and 7 the phase-correction data are converted into analogue form before being applied to the received phases. In the receiver of Figure 6 the received-phase signals are dephased .~ before multiplexing in accordance with the analogue phase-correction data. In the receiver of Figure 7 the phase-correction data are individually added to the received-phase data, converted into a convenient form for use.
:
10384~ ~
Fi~ures 6 and 7 otherwise have in common the elements shown at the top of these figures, namely the corrcction receiver, discriminator, 20 Hz filter, amplitude threshold ; detector and trigger. ~hese elements correspond otherwise to those in Figure 4, and they have the same r~eference number, except for the digit representing the hundreds, which stands for the number of the figure in each hlstance~
In Figure 6 the 20 ~z multiplexed phase-correction signal is applied to a demultiplexer 613 which receives the Omega format signals as a multiplexing instruction. '~he demultiplexer 613 is inhibited by the output of trigger 616 whenever the multiplexed signal amplitude passes below the threshold.
'~he outputs of the demultiplexer 613 are applied to a . , .
- 15 plurality of synchronous filters 614a to 614d. Each of these synchronous f-ilters contains a narrowband filter and a synchronous demodulator at 20 Hz which is controlled during the phase correction of the multiplexing segment to which it is allotted.
Such elements further contain a capacitor in their output stage, and so they are capable of the memory function with a time constant of the same order as that described ; with reference to ~igure 4. In actual fact, they also very often contain a veritable "phase memory".
In Figure 6 the Omega receiver supplies, for instance, received phases y M which are carried by a frequency of 1 ~z.
These phases are multiplexed due to the fact that they are 10384~
received at the same base frequency of the Gmega system.
They are applied to a multiplexed dephaser 621 which by other means receives the Omega segments and the synchronous phase-corrections 614 for application of each phase correction during the corresponding segment.
The output of the multiplexed dephaser 621 therefore - transmits signals which are at the frequency of 1 kMz and are corrected in phase. These signals are applied to a processing circuit 622, followed by a demultiplexer 623 and the channels 624a to 624_, these being standard circuits in an Omega receiver such as the one sold with the commercial -~
~ designation "NRNX lA" or "M2A" by S E R C E L.*
: Each synchronous filter 614 can contain the elements ~-~
-, ' 55 which are described by reference to Figure 6 in the above-mentioned patent, having regard to the fact that these elements also embody the demultiplexing function of the .` '~
circuit 613 of the present device.
The multiplexed dephaser 621 contains, for example, .,;
a fast-response dephaser, the phase shift instruction of which is multiplexed along the paths a, b, c, d.
For the third type of receiver, Figure 7 contains some elements which are analogous to those of Figure 6, namely, .~ the demultiplexer 713 and the synchronous filters 714_ to ;
714d.
The Omega reception part of Figure 7 contains a receiver circuit 727 with amplification, filtering and frequency-changing, followed by a demultiplexer 721, then by channels *Trademark for the Societe d'Etudes, Recherches et Constructions Electroniques ~'1, .
:
- . . E~. -~,: , . ' ' . ' ' ' ' 10384~3L :
722a to 722d in order to obtain received-phase data in a form which can be used directly.
In the t~e of receiver of Figure 7 the phase-correction data coming from the channels 714 is combined with the received-phase data arriving from the channels 722 in - the dephasers 723a to 72~. If the received phases from the ; channels 722 are carried by a frequency of ~ kHz~ then the circuits 723 are effective dephasers for this frequency.
If ~he received phases as well as the phase corrections are in analogue form, the circuits 723 can be analogue sub-tractors.
Clearly, in the embodiments illustrated in Figures 6 and 7 the action of the amplitude threshold detector and of the trigger is very important in enabling the memory function of the synchronous filters to play its role whenever the -~
carrier wave vanishes because of manipulation or, more parti~
cularly, because of sequential operation. The difference vis-à-vis Figure 4 resides in the fact that the read-out can be permanent in the receivers of Figures 6 and 7, the ; 20 frequeney controls contained in the narrowband synchronous filters here having a phase memory.
Experiments performed by the Applicant have shown that goniometric use of the carrier wave phase modulated by phase corrections in accordance with the invention is not affected by this phase modulation. This is true equally as well when the radiogoniometry is carried out with a moving-eoil receiver as when with more complicated receivers using -24~
. ~ ' .
- ~03848~L
a comparison between the wave received by a whip aerial "of reference" and the wave received by fixed crossed loops.
- However, the phase modulation can have a sli.ght influence on the intelliKibility of the i~entification signa]s . 5 of certain types of radio beacons.
: In particular, in aeronautical radio beacons with A1 type modulation the receivers generally use a beat frequ.ency :, osci].lator (B.F.O.) and the manipulation becomes evident by detectlon of the beat sig~al. In this case the effect of -~ 10 phase modulation in accordance with the invention will be perceptible in the form of a slight "vibrato" which cannot ~-nevertheless seriously affect the intelligibility of mani-,: , - pulated identification signals.
., , The studies and experiments of the ~pplicant ~elate .:; 15 especially to the possible influence of the modulation and manipulation characteristics necessary for operation of the radio beacon on the satisfactory functioning of "Differential ;~ Omega" correction receivers embodying the invention.
. Standard use of limiters upstream from the phase discriminator and careful filtering in the reception stages, properly speaking, already has the effect of sufficiently attenuating linear amplitude modulation whenever it exists.
In the event of intermodulations their effect on the correction carrier signals is further limited by reason of very effective filterlng of the multiplexed correction signal at 20 Hz and also in the subsequent synchronous demodu-lators, at least for the receivers of Figures 6 and 7.
.. .. . .. .. . .. .
. .
: ~
384~1 As regards the all-or-nothing modulation due to the ~ manipulation, the first experiments of the ~pplicant have `- shown that it has practically no perceptible effect on thè
transmission of "Differential Omega" corrections embodying the invention.
By contrast, the Applicant has paid particular atten-tion to defects which can be caused by periodical interruption of transmis~ion when only some of the radio beacons of a group are equipped for "Differential Omega" transmission, as is the case in ~igure 2. It will be considered that the ; -time allotted to each station is 1 minute, the period, or overall sequence time, here being 6 minutes.
Under these conditions the best result which may be obtainable duringr the "silences" of the transmission consists in keeping intact the correction values obtained during the most recent transmission in order to apply them throughout the interruption period due to these silences.
In fact, however, the correction values which should be applied, can vary significantly, whereas it is a constant value which is preserved.
The following Table gives some values observed by the .
Applicant for phase root mean-square errors expressed as a -percentage in turn for standing transmission or for various -cases of se~uential transmission.
The first row of the Table relates to approximate values associated only with the mode of transmission of the corrections in accordance with the invention, whilst the -26- ~-`.
- : .. , ., ~ . ... : , ~ 103848~L
~ second. row concerns the total error, allowing for the : fact that the corrections obtained at the selected site are not completely correlated with the corrections which should be made in all the zone where the~ are applied.
.~ 5 r~he root-mean-square error due to this decorrelation is generally evaluated to be about 1.5 percent when the . distance from the correction transmittlng station to the user is 300 km.
r~he th.ird row of the Table represents the degradation : 10 coefficient referred to sequential operation~ r~here is a ' slight degradation in standing transmission due to the fact . .
~ that the transmission is never perfect.
~ .
. . _ . . . ._ ._ .
:: . Standing Sequential Sequential, . transmission 1' on 2' period 3' .. . ._ . . ... :. _ _ 1' on 3' .
Root-mean-square deviation 0.216 1.04 2.15 .
... .. ... ... .. . _ ._ Root-mean-square error 1.51 1.83 2.62 ... __._ . .... _ . _ . . . . ~
Degradation .
coefficient 1.01 1.22 1.7 ~- .
It appears that standing transmission of "Differential Omega" corrections permits a 1:5 improvement in accuracy compared with the tabulated corrections defined by the Ame~iccm organization U.~. Naval Oceanographic Office. It is therefore clear that the values given in the above r~able for the two sequential modes of operation correspond also to distinctly better results than the tabulated corrections mentioned.
. ' ' ,10384~
This holds good for a range of 300 km from the selected site; beyond this range, it is preferable to use another correction transmitting station or to revert to the tabulated corrections.
. . .
... i ~, .
~ 5 For this purpose it is advantageous to use, jointly .. ..
- with a method embodying the present invention, the method ~
described in the French Patent 2,224,929, entitled ; -"Dispositif de correction de phase, notamment pour un recepteur de radionavigation Omega" (Phase correction device, notably for an Omega radionavigation receiver). The two .
, means can be used alternately, the corrections arriving from ~~ one or the other, or simultaneously, in which case the - corrections originating from the two means are then applied by two dephasers mounted in series to the phases received by the base Omega receiver. -; In this latter case, the correction device of the I ~ :
last-mentioned patent is not used for memory-storage of the U.S.N.O.O. tabulated corrections directly, but to contain differential values. These differential values are obtained by deducting the tabulated values relating to the site selected for measuring the "Differential Omega" ;
corrections transmitted and used, from the values of the - U.S.N.O.O. tabulated corrections for the location of the receiver.
~ ' ' ' :
,.
.' .
''' '~"
. . -: . ,
Claims (14)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of navigation in a sequential radio-navigation system by phase reception, applicable in differ-ential mode, with supplementary transmission of phase correc-tions defined by the difference between each phase received at a selected site and the corresponding theoretical phase as selected sequential transmissions in synchronous multi-plexed form, and with application of these corrections to the corresponding received phases, wherein a radiogoniometric carrier wave, amplitude modulated as an identification code, is modulated in phase or frequency, the said phase or frequency modulation being carried out by a multiplexed phase-correction signal having low frequency, and also having a phase which is so related linearly to the said phase corrections in succession that each phase correction appears approximately simultaneously with the phase to which it relates, and wherein the said carrier wave is received, filtered and demodulated in order to recover the multiplexed correction signal, and the said phase corrections contained in the multi-plexed correction signal are so applied to the received phases that each phase undergoes the phase correction which is received at the same instant as the phase.
2. A method in accordance with Claim 1, in which the said radiogoniometric carrier wave is interrupted, and another wave is thereupon transmitted at the same frequency from another transmitting station, wherein the said operation of phase or frequency modulation is effected with a multi-plexed phase-correction signal having at least one known multiplexing segment allotted to its reference phase, and at the said other transmitting station the said radiogonio-metric carrier wave is received, demodulated and filtered during the said known segment in order to extract therefrom the reference phase, and then the said phase or frequency modulation operation is repeated on the other wave with another multiplexed phase-correction signal at the said low frequency and having the said reference phase, the said operations of phase-correction reception and application then being performed on the other carrier wave modulated thus in phase or frequency.
3. A method in accordance with Claim 1 or 2, wherein the reception operation also includes narrowband filtering of the first low frequency of the correction signal, the said application of the phase corrections being inhibited whenever the amplitude of the signal thus filtered is less than a selected value.
4. A method in accordance with Claim 1, wherein the operation of phase-correction application possesses a self-hold time constant greater than 1 minute.
5. A method in accordance with Claim 4, wherein the application of the said phase corrections consists in heterodyning a signal derived from the received phases of the sequential radionavigation system with the said multi-plexed correction signal, the said time constant being applied to the phases then obtained after demultiplexing.
6. A method in accordance with Claim 4, wherein the application of phase corrections consists in demultiplexing the correction signal according to the format laid down locally for the phases of the sequential radionavigation system, the said time constant being applied to each demultiplexed phase correction in a corresponding synchronous filter, and in the phase shifting of a signal derived from the received phases of the sequential radionavigation system in multiplexed fashion as laid down in the local format and in accordance with the phase corrections arriving from the synchronous filters.
7. A method in accordance with Claim 4, wherein the application of phase corrections consists in demulti-plexing the correction signal according to the format laid down locally for the phases of the sequential system of radionavigation, the said time constant being applied to each demultiplexed phase correction in a corresponding synchronous filter, in separately demultiplexing the signal derived from the received. phases of the sequential system of radionavigation, and in individually applying the phase corrections to the corresponding phases thus demultiplexed.
8. A correction receiver for use with a receiver in a sequential radionavigation system comprising:
means for reception, filtering and demodulation of the carrier wave, thus recovering the multiplexed correction signal, means whereby the said phase corrections in the multiplexed correction signal are so applied to the received phases that each phase undergoes the phase correction received at the same instant, means for separately rectifying the said multiplexed correction signal, and means for inhibiting the application of corrections when the rectified amplitude of the multiplexed correction signal is less than a preselected value.
means for reception, filtering and demodulation of the carrier wave, thus recovering the multiplexed correction signal, means whereby the said phase corrections in the multiplexed correction signal are so applied to the received phases that each phase undergoes the phase correction received at the same instant, means for separately rectifying the said multiplexed correction signal, and means for inhibiting the application of corrections when the rectified amplitude of the multiplexed correction signal is less than a preselected value.
9. A correction receiver in accordance with Claim 8, wherein the means for application of the phase corrections possesses a self-hold time constant greater than 1 minute.
10. A correction receiver in accordance with Claim 8 or 9, wherein the means for application of the phase correc-tions contains a mixer which mixes the signal derived from the received phases of the sequential radionavigation system with the multiplexed correction signal, a demultiplexer and means for then recovering the individual received phases with the said time constant.
11. A correction receiver in accordance with Claim 8 or 9, wherein the means for application of the phase corrections contains a correction-signal demultiplexer, followed by a plurality of synchronous filters with the time constant precited for the individual phase corrections, and also a multiplexed dephaser for sequential phase shifts, according to the local format for the radionavigation receiver, of signals derived from the received phases by the latter, and in accordance with the phase corrections from the synchronous filters.
12. A correction receiver in accordance with Claim 8 or 9, for use with a radionavigation receiver supplying individual received phases, wherein the means for application of phase corrections contains a correction-signal demultiplexer, followed by a plurality of synchronous filters for recovery of the phase corrections with the precited time constant, and also a plurality of dephasers, each for modifying one received phase in accordance with the corresponding phase correction.
13. A correction receiver in accordance with Claim 8, additionally comprising means for generating phase-correction values as a function of time from recorded base values, and also means for applying these correction values to the received phases of the radionavigation system.
14. A correction receiver in accordance with Claim 13, wherein the two means for application of phase corrections are arranged for simultaneous action, the correction base values here being differential values, each equal to the difference between the correction in respect of the domain where the receiver is to be found and the correction for the selected site prescribed, defining the corrections transmitted.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR7324351A FR2236187B1 (en) | 1973-07-03 | 1973-07-03 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1038481A true CA1038481A (en) | 1978-09-12 |
Family
ID=9121966
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA203,817A Expired CA1038481A (en) | 1973-07-03 | 1974-07-02 | Transmission of radio navigation phase correction |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US3997902A (en) |
| JP (2) | JPS5817434B2 (en) |
| CA (1) | CA1038481A (en) |
| DE (1) | DE2432000C3 (en) |
| FR (1) | FR2236187B1 (en) |
| GB (1) | GB1480490A (en) |
| SE (1) | SE395967B (en) |
Families Citing this family (15)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS6053075U (en) * | 1983-09-21 | 1985-04-13 | 日本無線株式会社 | differential omega receiver |
| FR2561050B1 (en) * | 1984-03-07 | 1986-09-19 | Commissariat Energie Atomique | METHOD FOR MONITORING VEHICLE MOVEMENTS FROM A CENTRAL STATION |
| US4799062A (en) * | 1987-04-27 | 1989-01-17 | Axonn Corporation | Radio position determination method and apparatus |
| JPH01239492A (en) * | 1988-03-18 | 1989-09-25 | Komatsu Ltd | Moving body position measuring instrument by radio wave survey |
| US5365516A (en) * | 1991-08-16 | 1994-11-15 | Pinpoint Communications, Inc. | Communication system and method for determining the location of a transponder unit |
| RU2508968C2 (en) * | 2009-08-14 | 2014-03-10 | Сэнт-Гобэн Эбрейзивс, Инк. | Abrasive article (versions) and method of its forming |
| EP2464485A2 (en) | 2009-08-14 | 2012-06-20 | Saint-Gobain Abrasives, Inc. | Abrasive articles including abrasive particles bonded to an elongated body |
| TW201507812A (en) | 2010-12-30 | 2015-03-01 | Saint Gobain Abrasives Inc | Abrasive article and method of forming |
| WO2013040423A2 (en) | 2011-09-16 | 2013-03-21 | Saint-Gobain Abrasives, Inc. | Abrasive article and method of forming |
| KR20140075717A (en) | 2011-09-29 | 2014-06-19 | 생-고뱅 어브레이시브즈, 인코포레이티드 | Abrasive articles including abrasive particles bonded to an elongated substrate body having a barrier layer, and methods of forming thereof |
| TWI477343B (en) | 2012-06-29 | 2015-03-21 | Saint Gobain Abrasives Inc | Abrasive article and method of forming |
| TW201404527A (en) | 2012-06-29 | 2014-02-01 | Saint Gobain Abrasives Inc | Abrasive article and method of forming |
| TW201402274A (en) | 2012-06-29 | 2014-01-16 | Saint Gobain Abrasives Inc | Abrasive article and method of forming |
| TW201441355A (en) | 2013-04-19 | 2014-11-01 | Saint Gobain Abrasives Inc | Abrasive article and method of forming |
| TWI621505B (en) | 2015-06-29 | 2018-04-21 | 聖高拜磨料有限公司 | Abrasive article and method of forming |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1934960C3 (en) * | 1969-07-10 | 1979-01-25 | Prakla-Seismos Gmbh, 3000 Hannover | Method and arrangement for the precise location of points |
| FR2180549B1 (en) * | 1972-04-20 | 1977-01-14 | Sercel Rech Const Elect |
-
1973
- 1973-07-03 FR FR7324351A patent/FR2236187B1/fr not_active Expired
-
1974
- 1974-06-28 US US05/484,030 patent/US3997902A/en not_active Expired - Lifetime
- 1974-07-02 SE SE7408695A patent/SE395967B/en not_active IP Right Cessation
- 1974-07-02 CA CA203,817A patent/CA1038481A/en not_active Expired
- 1974-07-03 JP JP49075505A patent/JPS5817434B2/en not_active Expired
- 1974-07-03 GB GB29518/74A patent/GB1480490A/en not_active Expired
- 1974-07-03 DE DE2432000A patent/DE2432000C3/en not_active Expired
-
1982
- 1982-11-19 JP JP57202256A patent/JPS5899773A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5071287A (en) | 1975-06-13 |
| FR2236187B1 (en) | 1977-09-16 |
| JPS5899773A (en) | 1983-06-14 |
| FR2236187A1 (en) | 1975-01-31 |
| DE2432000B2 (en) | 1979-09-13 |
| GB1480490A (en) | 1977-07-20 |
| US3997902A (en) | 1976-12-14 |
| SE7408695L (en) | 1975-01-07 |
| DE2432000C3 (en) | 1980-06-04 |
| JPH025275B2 (en) | 1990-02-01 |
| AU7048674A (en) | 1976-01-08 |
| DE2432000A1 (en) | 1975-01-30 |
| JPS5817434B2 (en) | 1983-04-07 |
| SE395967B (en) | 1977-08-29 |
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